Fig. 7. Scanning electron micrographs of the precipitates formed at 1 M NH₄H₂PO₄, 10^-2 M Al, and pH 4.0 (a) in the absence of Fe(II) and (b) in the presence of Fe(II) at a Fe(II)/Al molar ratio = 1.2 after aging for 4 wk.

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